A magnetic disk device subjects data including a large number of high-frequency patterns to encoding processing in write processing. For example, a magnetic disk device subjects data including data patterns of 1T bits to encoding processing by the Non-Return to Zero (NRZ) system. When the magnetic disk is to write data including data patterns of 1T bits to a disk, a high degree of responsiveness is required of the magnetic disk device for the reason that the physical length of data to be written on the basis of a data pattern of 1T bits is short. Accordingly, when write data including data patterns of 1T bits is written to a disk, there is a possibility of the recording quality of the written data being lowered. In the case where the data the recording quality of which is lowered is read, there is a possibility of the magnetic disk device determining that a read error occurs when the data read from the disk is subjected to decoding processing.